feat: add MySQL database support with SQL translation

- Add MySQLConnection class with automatic SQL Server to MySQL translation
- Add connection factory to support both SQL Server and MySQL
- Update config schema to support MySQL configuration (host, port, db_type)
- Update default config to use MySQL (localhost:3306)
- Translate table names: [schema].[table] -> schema_table
- Translate placeholders: ? -> %s
- Translate MERGE statements to INSERT ... ON DUPLICATE KEY UPDATE

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

requirements.txt

@@ -8,6 +8,7 @@ playwright==1.57.0
 
 # --- Database ---
 pyodbc>=5.0.0
+mysql-connector-python>=8.0.0
 
 # --- Excel/Data Processing ---
 pandas>=2.0.0